Impact devices are often used in demolition, excavation, mining and the like endeavors, to break and separate material for easier removal One common impact device is an impact hammer, such as illustrated in U.S. Pat. No. 3,363,512 to Ottestad. Impact hammers generally include a fluid-driven, reciprocal piston which is struck against a spike or spade shaped tool element to penetrate and break up the material Although these hammers can be hand manipulated, they are usually mounted on the end of a boom of a carrier, such as a back hoe. These hammers are effective in penetrating hard materials, such as concrete or stone. However, the hammers generally only form a small bore or opening with each pass into the material. As a result, a number of passes are often required to effectively break and separate the material. Moreover, after the material is sufficiently broken, it must be removed by a bucket. The use of a bucket requires that the hammer be exchanged for the bucket or that an independent carrier with a bucket be used. These options undesirably increase the downtime and cost of the operation.
As can be appreciated, ordinary buckets do not form good devices for the break up and separation of hard material. Although the buckets can be struck against the material, it cannot match the speed or force of a conventional impact hammer. Further, buckets are not ordinarily fabricated to withstand these types of impact loads. To increase the penetration capacity of buckets, some artisans have coupled vibration inducing mechanisms to the front teeth of the bucket. Two examples of this type of construction are illustrated in U.S. Pat. No. 3,645,021 to Sonerud and West German Patent No. 24 37 468. These devices, however, have little effect when encountering a hard material
Impact buckets were specifically developed to perform the dual role of an impact hammer and a bucket. More particularly, impact buckets are buckets which have impact hammer units incorporated in their construction. The hammers are operatively connected to a movable front edge which acts as the impact tool element. Examples of such impact buckets are disclosed in U.S. Pat. Nos. 4,892,358 and 4,892,359 to Ottestad. These tools can effectively penetrate and separate pieces from a hard material. Further, the tool element is an elongated member which can quickly cut across an elongated portion of the material. Impact buckets also function to reduce the time and cost involved in completing a project by performing the two previously independent operations of breaking and removing the material with one device.
Nevertheless, the inclusion of the impact hammer into the bucket, has resulted in a significant reduction in the available bucket space for collection of the broken material. Heretofore, if more bucket space was desired, a smaller hammer unit was used. The use of a smaller hammer though produced less impact force. On the other hand, if a larger hammer unit was employed for greater impact force, bucket space was sacrificed.
Further, the positioning of a hammer within a bucket places constraints on orienting the impacting device with respect to the ground. Reference is had to FIG. 10 to better illustrate these design constraints. In particular, the bucket 1 is typically supported on the end of a boom by a pair of pins 2 and 3. One pin 2 (i.e., the one closer to the bucket opening) functions as the pivot point for bucket movement, while the force F for effecting movement of the bucket 1 is driven through the other pin 3. This operation causes the bucket 1 to move in an arcuate swinging motion, and thereby create a curved cut line C into the ground G. As can be appreciated, the bucket 1 must be designed so that its back corner 4 clears the curved cut line C.
The hammer 5 is positioned in the lower regions of the bucket so that the impact blade 6 lies along the front lip 7 of the bucket 1. The effectiveness of a hammer to break up hard ground (e.g., rock, frozen ground, etc.) depends upon the angle of attack and the crowd force being optimally set. The angle of attack A is defined as the angle which is formed by the intersection of the longitudinal axis of the impact blade and a line extending between the pivot axis (i.e., pin 2) and the tip of the impact blade. The crowd force is dependent on the ratio between the distance between the two pins L.sub.2 and distance between the pivot pin and the tip of the impact blade L.sub.1. As a result, these factors have limited the ability of designers to employ ever larger impact devices into buckets.
More specifically, the use of a more forceful hammer has heretofore required the hammer to have a correspondingly greater length. The increased hammer size has, in turn, resulted in an increased bucket depth An increase in the bucket depth, without further modifications to the bucket's design, would create clearance problems for the back corner 4 of the bucket 1 with respect to the cut line C. Hence, in order to accommodate the use of a larger hammer, the bucket must be reshaped such that the angle of attack A is lessened, the distance between the pivot pin and the blade tip L.sub.1 is lengthened or both In either case, the resulting changes to the angle of attack and/or crowd force offsets the increased power of the hammer in breaking up the ground.